GitLab

All implementations of ExtensionHostDelegate::GetExtensionHostQueue()
returned a singleton instance of an ExtensionHostQueue. Instead of this
piping, introduce ExtensionHostQueue::GetInstance(), which does the same
thing without needing to be implemented by the embedder.

TBR=atwilson@chromium.org (trivial background_contents.cc change)

Bug: 1028334
Change-Id: I339267c2a8193c27bd782b63a8f8cc5e15957be4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935489
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719395}